Cardiac probes are commonly used to measure and/or monitor cardiac output, blood flow, and stroke volume. Typically the probes include an ultrasonic transducer which is inserted into the heart via a catheter or is attached to the exterior of the heart. The transducer is coupled to an external circuit which applies a high frequency electrical signal that causes the transducer to transmit ultrasonic energy through a vessel in the heart. The energy reflected in the vessel is then received by the transducer and sent to the external circuitry for analysis and quantification.
These types of cardiac output probes are often attached outside the pulmonary artery immediately following open heart surgery to measure and monitor cardiac output. Since the probe is connected to external circuitry and instrumentation, the chest is typically left open during the monitoring procedure, thereby restricting the time period after completion of the surgery during which these measurements can be made.